The present invention relates generally to a valve, and more particularly to a valve having a housing and a rotational body, such as a spherical rotational body, arranged rotatably therein.
A ball valve is described in EP 1 047 894 B1 having a separately embodied shaft mechanically linked to a spherical rotational body of the valve. The rotational body includes a passage for a flow medium. The interior of a housing includes two seat rings that are spaced apart in the direction of flow. The rings are sealingly positioned against the outer spherical surface of the rotational body. A rectangular part of the shaft engages in a correspondingly embodied seat of the rotational body and is conducted through an opening in the housing to the outside. The rotational body may be rotated by means of a lever or the like into the desired position for closing or at least partially opening the flow path. Because the rotational body and shaft are embodied as two parts, in the closed position the floatingly arranged rotational body is pressed more strongly against the downstream seat ring due to a difference in pressure. Also, movements of the rotational body caused by the flow medium or the differences in pressure are to be kept away from the shaft. In the area of the housing opening the shaft includes a part having a spherical outer surface against which is positioned a sealing element arranged in the housing. The sealing effect of the sealing element is heightened by the pressure of the flow medium in the housing interior enhancing the so-called external seal. It is intended that the spherical outer surface of the aforesaid shaft part will ensure that the external seal will not be negatively affected by axial movements of the shaft or by pivot movements introduced from outside, such as by the lever. It has been found that due to the embodiment of rotational body and shaft in two parts, practically no pivot movements or at least only negligible pivot movements, are exerted on the shaft.
A ball valve is also described in DE 30 23 230 A1, in which a rotational body and shaft are embodied integrally. The inner surfaces of a housing, which surfaces receive the spherical rotational body and the shaft, are provided with a common liner or coating made of plastic. The outer surfaces of the rotational body and the shaft embodied integrally therewith are also provided with a coating or liner made of plastic. A gland packing seal is arranged in the housing opening for the shaft for sealing purposes. Because the shaft and the rotational body are integrally embodied, forces are transmitted directly onto the shaft by the flow medium or by differences in pressure, especially when the rotational body is in the closed position. The result is that local load peaks and quite high surface pressures occur between the shaft liner and the gland packing. These shorten the tool life and service life and can lead to elevated leak rates, even after relatively short operating times.
Another valve is described in EP 0 809 059 B1 having a housing interior provided with a plastic liner. A rotational body and shaft likewise have a liner or coating made of plastic. The rotational body is borne floating in the housing by means of support rings arranged spaced apart in the direction of flow. The inner end of the shaft, which shaft is provided with the aforesaid liner or coating at least in the interior of the housing, engages in a correspondingly embodied recess of the rotational body. The recess also is lined with plastic. The shaft being engaged in the recess can rotate the rotational body for closing or opening the flow path. Sufficient clearance between the aforesaid recess of the floatingly borne rotational body and the engaging shaft end is required to prevent axial movements from being transmitted to the shaft, especially axial movements due to differences in pressure or pressure fluctuations in the flow medium. Production and manufacture of the aforesaid connection requires complexity that is not insignificant. Furthermore, hysteresis and/or positional differences between the angle of rotation position for the shaft and the angle of rotation position for the rotational body may occur, which are disadvantages. These disadvantages are especially noteworthy for a control valve and/or in automated systems in which drives are provided that are suitable for rotating the shaft and ultimately the rotational body. Still further, a special double seal provided in the area of the shaft opening requires a not insignificant structural volume and correspondingly complex production and assembly.
Accordingly, there is a need for a valve with low structural complexity capable of avoiding the aforesaid disadvantages and having a long tool life and long service life. There also is a need for a valve capable of tolerating aggressive flow media that can avoid damage from such media's corrosive effects and/or from external influences such as ambient humidity. Moreover, disadvantageous influences on the sealing of the shaft are to be avoided. Accordingly, an object of the present invention is to provide a valve that is functionally reliable having optimized sealing and a longer tool life, especially when used at high pressures or high temperatures.